best materials for the run?

i am new to chickens! we are currently keeping the chickens in my grandparents shed until our house is finished, but we are getting close and plan on making a run for their little coop. what kind of flooring do you prefer and why? i dont even know where to start. ive heard of many different things but want to know whats good for what reasons
i live in utah so we get super hot summers and really cold winters. so any tips for winter hitting would be helpful as well. like do certain floorings freeze easy? like sand, saw dust?, wood shavings? i dont know what will be best or easiest to keep clean or low maintainance anyway. i would like to just use the plain ol dirt that is already there but dont know how that will effect the smell since it will be just below the deck. or if it would effect it when we lay grass in the spring, like all i can think of is masses of chicken poop gumming up the grass haha at least where the run is.

Make sure the run is not at a low point that collects rain runoff. I have natural dirt ground and little smell. Chicken poop will decompose quickly and blend with the dirt as they scratch. Not saying it will be pristine, but not filthy.